Essentially, two construction variants of fuel cells are known in the state of the art. This on the one hand relates to stacked fuel cells (fuel cell stacks) which have a first air pump for cathode supply as well as a further fan for air cooling or a fluid cooling circuit for the cooling the fuel cells themselves. One example of such a fuel cell arrangement is U.S. Pat. No. 6,503,650 B1, which shows a water circuit which amongst other things cools the fuel cells themselves. The fuel cell arrangement has a ventilation unit with two fans which may blow or suck a gas flow into the cathode of a fuel cell in different directions, in order to ensure a ventilation of the cathode. For this purpose, a gas flow divider may be varied in its position, in order to find the suitable air distribution. With this, the gas flow is sucked in a region defined by the gas flow divider or blown through the cathode. It is ensured that the humidity of the cathode side, which is important for the functioning of the fuel cell, is not completely carried away out of the cathode, by way of setting the intensity of the blowing or sucking gas flow. At the same time however, one takes care that enough fresh air reaches the cathode. The disadvantage of this arrangement is the complicated construction and the energy-intensive operation of the fuel cell arrangement.
A further example of a structure for an efficient gas exchange is known from U.S. Patent Publication No. 2006/0269821 A1, which shows a fuel cell stack having at one of its sides a gas channel which is closed at one side and on which cathode channel openings connect in a manner such that the air introduced into the gas channel is blown out completely through the cathode channels and thus effects a gas exchange at the cathodes. The disadvantage of this arrangement is that the gas channel for leading the gas flow subsequently led into the cathode channels, must be weak, so that no humidity is led away out of the cathode channels and thus the efficiency of the fuel cell arrangement is not reduced.
These active systems are only suitable from a minimum power of approx. 10 Watt, since otherwise the peripheral components, i.e. the fan or the cooling components are no longer available in the necessary miniaturization, create costs which are too high in relation to the power density, lower the reliability of the system or themselves consume too much energy.
The second basic construction variant is the one planar, completely passive fuel cell, with which the reactant exchange at the cathode is effected alone by way of natural convection.
Such fuel cells are preferably applied in as small as possible miniaturized systems. The disadvantage of such fuel cells however is the large limitation of the power density and the dependency on the external conditions.